Method of forming sidewall spacers to reduce formation of recesses in the substrate and increase dopant retention in a semiconductor device

ABSTRACT

A method of forming sidewall spacers for a gate in a semiconductor device includes re-oxidizing/annealing silicon of the substrate and silicon of the gate after formation of the gate. The substrate is re-oxidized by performing an anneal in an inert atmosphere or ambient. The substrate may be re-oxidized/annealing after depositing an oxide layer covering the substrate and gate. Additionally, the substrate may be re-oxidized/annealing after forming the gate without depositing the oxide layer.

FIELD

This invention relates generally to semiconductor fabrication.

BACKGROUND

As CMOS technology continues to scale further into the sub-micron region, the width of the gate on metal oxide semiconductor (MOS) transistors and the thickness of the gate oxide are constantly being reduced MOS transistors gates are formed using a conductive material such as metals, silicides, and doped polycrystalline silicon (polysilicon). For MOS transistor gates formed using doped polysilicon, metal silicides are often formed on the gate structure to reduce the sheet resistance of the gate and to ensure proper electrical contract.

The self-aligned process used to fabricate MOS transistors and other processes require the formation of a sidewall structure. Along with the reduction in MOS transistor gate width, the scaling of CMOS technology also requires that the width of the sidewall structures be reduced. Gate fabrication techniques utilize an etching process, such as plasma etching or wet chemical etching, to chemically remove material to form the microelectronic devices.

Some etching processes used in fabricating the gate remove material that would otherwise be beneficial to the construction or operation of the microelectronic device. For example,as illustrated in FIG. 4A, a polysilicon gate 402 including a thin gate oxide layer 403 are formed on a substrate 404. To form sidewall, a oxide layer 406 and a nitride layer 408 are formed over gate 402 and substrate 404. As illustrated in FIG. 4B, to form the gate sidwalls, nitride layer 408 is typically etched by using a plasma etch process which does not completely stop on oxide layer 406, but etches away oxide layer 406 and a portion of substrate 404 creating a recess 410 in substrate 404. Additionally, as illusrated in FIG. 4B, a subsequent oxidation step, which is used to remove the plasma etch damage, increases recess 410 because part of the silicon in substrate 404 gets converted to silicon oxide 410. The oxidation step is also referred to as the poly-oxidation or “smile” oxidation step because it creates a “smile” oxide 412 at the edge of the gate. The oxidation step is followed by the offset spacer loop.

The recess in the substrate can degrade the performance of the transistor and increase its variability. A thick smile oxide can reduce overlap capacitance and reduce transistor drive current. It is therefore desirable to minimize the silicon recess and “smile oxide” in the fabrication of the transistor structure. This present teachings provide several fabrication techniques to minimize the recess and smile oxide and improve performance.

SUMMARY

An embodiment of the present disclosure is directed to a method of fabricating a semiconductor device. The method comprises forming a polysilicon gate on an active region of the semiconductor device. The method also comprises depositing an oxide layer covering the gate, re-oxidizing a portion of the polysilicon of the gate and the silicon substrate to grow a thin silicon oxide layer on the gate and substrate, forming a sidewall layer covering the oxide layer, and removing portions of the sidewall layer and the oxide layer to from spacers on sidewalls of the gate.

Another embodiment of the present disclosure is directed to a method of fabricating a semiconductor device. The method comprises forming a gate on an active region of the semiconductor device. The gate comprises polysilicon. The method also comprises re-oxidizing a portion of the polysilicon of the gate to form a silicon oxide layer on the gate, forming a sidewall layer covering the oxide layer, and removing portions of the sidewall layer and the oxide layer to from spacers on sidewalls of the gate.

Additional embodiments of the disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present disclosure. The embodiments of the disclosure will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description, serve to explain the principles of the embodiments.

FIG. 1A and 1B are flow diagrams illustrating a semiconductor fabrication method consistent with embodiments of the present disclosure.

FIGS. 2A-2F and 3A-3E are diagrams illustrating a semiconductor fabrication method consistent with embodiments of the present disclosure.

FIGS. 4A and 4B are diagrams illustrating a conventional secmiconductor fabrication method.

DETAILED DESCRIPTION

According to embodiments of the present disclosure, a method of forming sidewall spacers can reduce formation of recesses in the substrate of a semiconductor device and can minimize the amount of smile of the gate. In the method, silicon of the substrate and polysilicon of the gate is re-oxidized/annealed after formation of the gate. The substrate and gate are re-oxidized by performing an anneal in an inert atmosphere or ambient. The substrate and gate may be re-oxidized/annealed after depositing an oxide layer covering the gate. Additionally, the substrate and gate may be re-oxidized/annealed after forming the gate without depositing the oxide layer.

By re-oxidation/anneal, the method reduces recesses formed in the substrate during fabrication. By decreasing recess in the substrate, the performance of semiconductor device is improved. Further, the re-oxidation/anneal densifies the oxide layer making it resistant to etch processes, drives in dopants trapped near the surface, and reduces thickness variations in the oxide layer.

Reference will now be made in detail to the exemplary embodiments of the present disclosure, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

In the following description, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration specific exemplary embodiments which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the invention. The following description is, therefore, merely exemplary.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein are to be understood to encompass any and all sub-ranges subsumed therein. For example, a range of “less than 10” can include any and all sub-ranges between (and including) the minimum value of zero and the maximum value of 10, that is, any and all sub-ranges having a minimum value of equal to or greater than zero and a maximum value of equal to or less than 10, e.g., 1 to 5.

According to embodiments of the present disclosure, a semiconductor fabrication process may include a method of forming sidewall spacers that reduces formation of recess in the substrate of a semiconductor device. FIG. 1A is a flow diagram illustrating a method 100 for forming sidewall spacers according to embodiments of the present disclosure. In method 100, portions of the polysilicon gate and the silicon substrate are re-oxidized after formation of the gate. The substrate and gate are re-oxidized by performing an anneal in an oxidizing/inert atmosphere. The substrate and gate may be re-oxidized/annealed after depositing an oxide layer covering the gate.

Method 100 begins with a gate of a semiconductor device being formed on a substrate (stage 102). The substrate may be any type of substrate on which the semiconductor device, such as a MOSFET, may be formed. For example, the substrate may be a silicon wafer, a silicon wafer with previously embedded devices, an epitaxial layer grown on a wafer, a semiconductor on insulation (“SOI”) system, or other suitable substrates having any suitable crystal orientation.

The gate may be formed using any suitable growth and/or deposition techniques available in semiconductor processing and may be formed of any suitable material or combination of materials. For example, the gate may be formed by depositing or growing a gate insulator layer on the substrate and forming a gate material layer or layers on the gate insulator layer. Then, the gate insulator layer and gate material layer may be patterned and portions removed using suitable and well-known techniques, such as etching, polishing, and the like, to form the gate. One skilled in the art will realize that the gate may include additional well-known components.

Next, an ion implantation is performed to create a source region and a drain region on either side of the gate (stage 104). The ion implantation may be performed using any suitable techniques available in semiconductor processing and any suitable dopant to form the source and drain regions.

The ion impanation stage may optionally performed after forming the gate. One skilled in the art will realize that the ion implantation may be performed at any stage during the semiconductor fabrication process.

Then, an oxide layer is formed to cover the gate and portions of the substrate (stage 106). According to embodiments of the present disclosure, the oxide layer is utilized during the re-oxidation/anneal of the gate and substrate. Additionally, the oxide layer is utilized as part of sidewall spacers of the gate. The oxide layer may be formed using any suitable growth and/or deposition techniques available in semiconductor processing and may be formed from any suitable material or combination of materials.

Next, the silicon of the substrate and the polysilicon of the gate can be re-oxidize/anneal to form a re-oxidized layer (stage 108). Re-oxidation/anneal may be achieved using any suitable method to form a re-oxidized layer in the materials of the substrate and gate. For example, an anneal, such as a rapid thermal anneal, spike anneal, ultra-high temperate anneal or combination thereof, may be performed in an inert atmosphere or ambient.

By re-oxidizing/annealing the substrate, method 100 reduces recesses formed in the substrate during fabrication. By preventing recesses in the gate, the performance of the semiconductor device may be increased. Further, the re-oxidation/anneal densities the oxide layer making it resistant to etch processes. Moreover, by re-oxidizing/annealing the substrate, dopants trapped near the surface of the substrate can be driven in rather than lost.

Then, a sidewall layer is formed covering the gate and portions of the substrate (stage 110). The sidewall layer may be formed using any suitable growth and/or deposition techniques available in semiconductor processing and may be formed from any suitable material or combination of materials.

After that, portions of the sidewall layer and the oxide layer are removed (stage 112). The portions are removed in order to from spacers on the sidewall of the gate. Additionally, the portions are removed in order to expose the substrate and the top of the gate. Portions of the sidewall layer and the oxide layer may be removed using any suitable material removal techniques available in semiconductor processing, such as etch processes.

One skilled in the art will realize that additional semiconductor fabrication processes may be performed to complete the semiconductor device. Additionally, one skilled in the art will realize that additional semiconductor device may be fabricated to operate with the semiconductor device fabricated by method 100.

FIG. 1B is a flow diagram illustrating a method 150 for forming sidewall spacers according to other embodiments of the present disclosure. In method 150, the silicon of the substrate and the polysilicon of the gate is re-oxidized after formation of the gate. The substrate and gate are re-oxidized by performing an anneal in an inert atmosphere or ambient. The substrate and gate are re-oxidized/annealed after forming the gate without first depositing an oxide layer.

Method 150 begins with a gate of a semiconductor device being formed on a substrate (stage 152). The substrate may be any type of substrate on which the semiconductor device, such as a MOSFET, may be formed. For example, the substrate may be a silicon wafer, a silicon wafer with previously embedded devices, an epitaxial layer grown on a wafer, a SOI system, or other suitable substrates having any suitable crystal orientation.

The gate may be formed using any suitable growth and/or deposition techniques available in semiconductor processing and may be formed of any suitable material or combination of materials. For example, the gate may be formed by depositing or growing a gate insulator layer on the substrate and forming a gate material layer or layers on the gate insulator layer. Then, the gate insulator layer and gate material layer may be patterned and portions removed using suitable and well-known techniques, such as etching, polishing, and the like, to form the gate. One skilled in the art will realize that the gate may include additional well-known components.

Next, an ion implantation is performed to create a source region and a drain region on either side of the gate (stage 154). The ion implantation may be performed using any suitable techniques available in semiconductor processing and any suitable dopant to form the source and drain regions.

The ion impanation stage may optionally performed after forming the gate. One skilled in the art will realize that the ion implantation may be performed at any stage during the semiconductor fabrication process.

Next, the silicon of the substrate and polysilicon of the gate can be re-oxidize/anneal to form a re-oxidized layer in the gate and substrate (stage 156). Re-oxidation may be achieved using any suitable method to form a re-oxidized layer in the materials of the gate and substrate. For example, an anneal may be performed in an inert atmosphere or oxidizing ambient.

By re-oxidizing/annealing the substrate and the gate, method 150 reduces recesses formed in the substrate during fabrication. By preventing recesses in the gate, the performance of the semiconductor device may be increased.

Additionally, during the re-oxidization/anneal, an oxide layer may be formed to cover the gate and portions of the substrate. The oxide layer may be formed from any suitable material or combination of materials depending on the material of the gate and substrate and the anneal performed to re-oxidize the gate and substrate.

Then, a sidewall layer is formed covering the gate and portions of the substrate (stage 158). The sidewall layer may be formed using any suitable growth and/or deposition techniques available in semiconductor processing and may be formed from any suitable material or combination of materials.

After that, portions of the sidewall layer and the oxide layer (if formed) are removed (stage 160). The portions are removed in order to from spacers on the sidewall of the gate. Additionally, the portions are removed in order to expose the substrate and the top of the gate. Portions of the sidewall layer and the oxide layer (if formed) may be removed using any suitable material removal techniques available in semiconductor processing, such as etch processes.

One skilled in the art will realize that additional semiconductor fabrication processes may be performed to complete the semiconductor device. Additionally, one skilled in the art will realize that additional semiconductor device may be fabricated to operate with the semiconductor device fabricated by method 150.

As mentioned above, the method of forming sidewalls spacers may be utilized in forming a semiconductor device such as a MOSFET. FIGS. 2A-2F are diagrams illustrating a method for forming a MOSFET 200 including sidewall spacers.

FIG. 2A is a generalized diagram illustrating MOSFET device 200 such as a NMOS, PMOS, CMOS, or other suitable semiconductor device. As illustrated, MOSFET 200 includes a buried oxide layer 202, substrate 204, and a gate 206. It should be readily apparent to those of ordinary skill in the art that MOSFET 200 illustrated in FIG. 2A represents a generalized illustration and that other components may be added or existing components may be removed or modified. Further, MOSFET 200 may be part of an integrated circuit which includes other semiconductor devices.

Buried oxide layer 202 may be formed from any suitable oxide material. Likewise, substrate 204 may be formed from any suitable semiconductor material, such as silicon. For example, substrate 204 may be a silicon wafer with an oxide layer 202, such as silicon dioxide (SiO₂), buried in the silicon wafer.

Substrate 204 may include an active region formed under gate 206. The active region may be either an N-type active region or a P-type active region depending on the particularly type of MOSFET 200. The well region may be formed using any suitable techniques used in semiconductor processing, such as ion implantation.

Gate 206 may include a gate insulator 208 and gate material 210. Gate 206, including gate insulator 208 and gate material 210, may be formed from any suitable material or combination of materials. For example, gate insulator 208 may be formed of SiO₂, nitrided SiO₂, Hafnium Oxide (HfO₂), Hafnium Silicate (HfSiO₄), and the like. For example, gate material 210 may be formed of polysilicon and the like.

Gate 206 may be formed using any suitable growth and/or deposition techniques available in semiconductor processing. For example, gate 206 may be formed by depositing or growing a gate insulator layer on substrate 204 and forming a gate material layer on the gate insulator layer. Then, the gate insulator layer and gate material layer may be patterned and portions removed using suitable and well-known techniques to form a MOSFET gate. One skilled in the art will realize that gate 206 is exemplary and that gate 206 may include additional well-known components.

As illustrated in FIG. 2B, after formation of the gate 206, and source region 212, including a source, and drain region 214, including a drain, may be formed on either side of gate 206 by an ion implantation process 215. Both source region 212 and drain region 214, respectively, may be formed using any suitable techniques available in semiconductor processing, such as ion implantation. For example, boron or other suitable P-type dopant may be implanted during the ion implantation process to form source region 212 and the drain region 214. If MOSFET 200 is an N-type transistor, then arsenic, phosphorous, antimony, or other suitable N-type dopant may be implanted in substrate 204 during the ion implantation process to form source region 212 and drain region 214.

Although not illustrated in FIG. 2B, both source region 212 and the drain region 214 may have heavily doped and lightly doped regions. After the ion implantation in source region 212 and the drain region 214, an anneal process may be performed for diffusion of the dopant. One skilled in the art will realize that this anneal process may be carried out at any suitable temperature for any suitable time period.

As illustrated in FIG. 2C, after forming source region 212 and the drain region 214, an oxide layer 216 may be formed to cover gate 206 and portions-of substrate 204. Oxide layer 216 may be formed using any suitable growth and/or deposition techniques available in semiconductor processing and may be formed from any suitable material or combination of materials.

Oxide layer 216 may be formed to any suitable thickness to affect the re-oxidation of gate material 210 and serve as a spacer on gate 206. For example, oxide layer 216 may be formed to a thickness ranging from approximately 20 Å to 70 Å.

As illustrated in FIG. 2D, after forming oxide layer 216, gate material 210 of gate 206 and oxide layer 216 can be subjected to a re-oxidized/anneal process 219. Re-oxidation/anneal process 219 may be achieved using any suitable method to from a re-oxidized layer 218. For example, an anneal, such as a rapid thermal anneal, spike anneal, ultra-high temperate anneal or combination thereof may be performed in an inert atmosphere or oxidizing ambient.

One skilled in the art will realize that this anneal process may be carried out at any suitable temperature for any suitable time period. For example, a spike anneal can be carried out at about 900 degrees C. to about 1000 degrees C., or a flash/laser anneal can be carried out at about 1150 degrees C. to about 1400 degrees C.

Re-oxidized layer 218 may be formed to any suitable thickness. For example, re-oxidized layer 218 may be formed to approximately 5 Å.

By re-oxidizing/annealing the substrate, recesses formed in the substrate during fabrication may be reduced. By preventing recesses in the gate, the performance of the semiconductor device may be increased. Further, the re-oxidation/anneal densifies the oxide layer making it resistant to etch processes. Moreover, by re-oxidizing/annealing the substrate, dopants trapped near the surface of the substrate can be driven in rather than lost.

As illustrated in FIG. 2E, after re-oxidation, a sidewall layer 220 may be formed to cover oxide layer 216 over gate 206 and portions of substrate 204. Sidewall layer 220 may be formed from any suitable material or combination of materials. For example, sidewall layer 220 may be formed of silicon nitride (SiN), silicon carbide (SiC), silicon carbo-nitride (SiCN), silicon oxy-nitride (SiON), silicon oxy-carbide (SiOC), silicon oxy-carbo-nitride (SiOCN), and combinations thereof.

Sidewall layer 220 may be formed using any suitable growth and/or deposition techniques available in semiconductor processing. For example, sidewall layer 220 may be formed by chemical vapor deposition (CVD), atmospheric pressure CVD (APCVD), Low Pressure CVD (LPCVD), plasma enhanced CVD (EPCVD), rapid thermal CVD (RTCVD), metal-organic CVD (MOCVD), physical vapor deposition (PVD), and the like.

As illustrated in FIG. 2F, after formation of sidewall layer 220, portions of sidewall layer 220 and oxide layer 216 may be removed to form spacers 222. Spacers 222 may be formed using any suitable material removal techniques available in semiconductor processing. For example, sidewall layer 220 and oxide layer 216 may be selectively removed by one or more etch processes, such as wet etch, dry etch, anisotropic etch, and the like, to expose a top portion of gate 206, source region 212, and drain region 214. One skilled in the art will realize that this etch process may be carried out using any suitable chemical for any suitable time period to form spacers 222.

In the process described above with reference to FIGS. 2A-2F, source region 212 and drain region 214 may be formed after forming gate 206 and prior to re-oxidizing gate 206. One skilled in the art will realize that source region 212 and drain region 214 may be formed at any stage during the process including, but not limited, after formation of spacers 222.

As mentioned above, a substrate may be re-oxidized without first forming a gate oxide layer. FIGS. 3A-3E are diagrams illustrating a method for a MOSFET device 300 including sidewall spacers.

FIG. 3A is a generalized diagram illustrating MOSFET device 300 such as a NMOS, PMOS, CMOS, or other suitable semiconductor device. As illustrated, MOSFET 300 includes a buried oxide layer 302, substrate 304, and a gate 306. It should be readily apparent to those of ordinary skill in the art that MOSFET 300 illustrated in FIG. 3A represents a generalized illustration and that other components may be added or existing components may be removed or modified. Further, MOSFET 300 may be part of an integrated circuit which includes other semiconductor devices.

Buried oxide layer 302 may be formed from any suitable oxide material. Likewise, substrate 304 may be formed from any suitable semiconductor material, such as silicon. For example, substrate 304 may be a silicon wafer with an oxide layer 302, such as silicon dioxide (SiO₂), buried in the silicon wafer.

Substrate 304 may include an active region formed under gate 306. The active region may be either an N-type active region or a P-type active region depending on the particularly type of MOSFET 300. The well region may be formed using any suitable techniques used in semiconductor processing, such as ion implantation.

Gate 306 may include a gate insulator 308 and gate material 310. Gate 306, including gate insulator 308 and gate material 310, may be formed from any suitable material or combination of materials. For example, gate insulator 308 may be formed of SiO₂, nitrided SiO₂, HfO₂, HfSiO₄, and the like. For example, gate material 310 may be formed of polysilicon and the like.

Gate 306 may be formed using any suitable growth and/or deposition techniques available in semiconductor processing. For example, gate 306 may be formed by depositing or growing a gate insulator layer on substrate 304 and forming a gate material layer on the gate insulator layer. Then, the gate insulator layer and gate material layer may be patterned and portions removed using suitable and well-known techniques to form a MOSFET gate. One skilled in the art will realize that gate 306 is exemplary and that gate 306 may include additional well-known components.

As illustrated in FIG. 3B, after formation of the gate 206, and source region 312, including a source, and drain region 314, including a drain, may be formed on either side of gate 306 by an ion implantation process 315. Both source region 312 and drain region 314, respectively, may be formed using any suitable techniques available in semiconductor processing. For example, boron or other suitable P-type dopant may be implanted during the ion implantation process to form source region 312 and the drain region 314. If MOSFET 300 is an N-type transistor, then arsenic, phosphorous, antimony, or other suitable N-type dopant may be implanted in substrate 304 during the ion implantation process to form source region 312 and drain region 314.

Although not illustrated in FIG. 3B, both source region 312 and the drain region 314 may have heavily doped and lightly doped regions. After the ion implantation in source region 312 and the drain region 314, an anneal process may be performed for diffusion of the dopant. One skilled in the art will realize that this anneal process may be carried out at any suitable temperature for any suitable time period.

As illustrated in FIG. 3C, after forming source region 312 and drain region 314, gate material 310 of gate 306 is subjected to a re-oxidized/anneal process 319. Re-oxidation/anneal process 319 may be achieved using any suitable method to from a re-oxidized layer 316 in gate material 210. For example, an anneal, such as a rapid thermal anneal, spike anneal, ultra-high temperate anneal or combination thereof, may be performed in an inert or ambient oxidizing atmosphere.

One skilled in the art will realize that this anneal process may be carried out at any suitable temperature for any suitable time period. For example, a spike anneal can be carried out at about 900 degrees C. to about 1000 degrees C., or a flash/laser anneal can be carried out at about 1150 degrees C. to about 1400 degrees C. Re-oxidized layer 316 may be formed to any suitable thickness.

During the anneal, an oxide layer 318 may be formed on the substrate and portions of gate 306. Oxide layer 318 may be formed to any suitable thickness that may be achieved during the anneal process. For example, oxide layer 318 may be formed to a thickness ranging from approximately 20 Å to 70 Å.

By re-oxidizing/annealing the substrate, recesses formed in the substrate during fabrication may be reduced. By preventing recesses in the gate, the performance of the semiconductor device may be increased. Further, the re-oxidation/anneal densifies the oxide layer making it resistant to etch processes. Moreover, by re-oxidizing/annealing the substrate, dopants trapped near the surface of the substrate can be driven in rather than lost.

As illustrated in FIG. 30, after re-oxidation/anneal, a sidewall layer 320 may be formed to cover oxide layer 318 over gate 306 and portions of substrate 304. Sidewall layer 320 may be formed from any suitable material or combination of materials. For example, sidewall layer 320 may be formed of SiN, SiC, SiCN, SiON, SiOC, SiOCN, and combinations thereof.

Sidewall layer 320 may be formed using any suitable growth and/or deposition techniques available in semiconductor processing. For example, sidewall layer 320 may be formed by CVD, APCVD, LPCVD, EPCVD, MOCVD, RTCVD, PVD, and the like.

As illustrated in FIG. 3E, after formation of sidewall layer 320, portions of sidewall layer 320 and oxide layer 318 may be removed to form spacers 322. Spacers 322 may be formed using any suitable material removal techniques available in semiconductor processing. For example, sidewall layer 320 and oxide layer 318 may be selectively removed by one or more etch processes, such as wet etch, dry etch, anisotropic etch, and the like, to expose a top portion of gate 306, source region 312, and drain region 314. One skilled in the art will realize that this etch process may be carried out using any suitable chemical for any suitable time period to form spacers 322.

In the process described above with reference to FIGS. 3A-3E, source region 312 and drain region 314 may be formed after forming gate 306 and prior to re-oxidizing gate 306. One skilled in the art will realize that source region 312 and drain region 314 may be formed at any stage during the process including, but not limited, after formation of spacers 322.

Other embodiments of the present disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims. 

1. A method of fabricating a semiconductor device, comprising: forming a gate on an active region of the semiconductor device, wherein the gate comprises polysilicon; forming an oxide layer covering the gate; re-oxidizing a portion of the polysilicon of the gate to form a silicon oxide layer on the gate; forming a sidewall layer covering the oxide layer; and removing portions of the sidewall layer and the oxide layer to from spacers on sidewalls of the gate.
 2. The method of claim 1, further comprising performing an ion implantation after etching the sidewall and oxide layers.
 3. The method of claim 1, further comprising performing an ion implantation prior to depositing the oxide layer.
 4. The method of claim 1, wherein re-oxidizing the polysilicon comprises performing an anneal in an inert or oxidizing ambient atmosphere.
 5. The method claim 4, wherein performing an anneal comprises performing at least one of a rapid thermal anneal, spike anneal, and ultra-high temperate anneal.
 6. The method of claim 4, wherein performing an anneal comprises performing a spike anneal at a temperature of about 900 degrees C. to about 1000 degrees C.
 7. The method of claim 4, wherein performing an anneal comprises performing a flash/laser anneal at a temperature of about 1150 degrees C. to about 1400 degrees C.
 8. The method of claim 1, wherein forming the gate comprises: depositing a gate oxide layer adjacent to the active region; depositing polysilicon layer adjacent to the gate oxide layer; and removing portions the gate oxide layer and the polysilicon layer to form the gate.
 9. The method of claim 1, wherein the oxide layer is formed to a thickness ranging from approximately 20 Å to 70 Å.
 10. The method of claim 1, wherein the silicon oxide layer is formed to a thickness of approximately 5 Å.
 11. The method of claim 1, wherein the sidewall layer is formed of at least one material selected from the group consisting of silicon nitride (SiN), silicon carbide (SiC), silicon carbo-nitride (SiCN), silicon oxy-nitride (SiON), silicon oxy-carbide (SiOC), and silicon oxy-carbo-nitride (SiOCN).
 12. A method of fabricating a semiconductor device, comprising: forming a gate on an active region of the semiconductor device, wherein the gate comprises polysilicon; re-oxidizing a portion of the polysilicon of the gate to form a silicon oxide layer on the gate; forming a sidewall layer covering the oxide layer; and removing portions of the sidewall layer and the oxide layer to from spacers on sidewalls of the gate.
 13. The method of claim 12, further comprising performing an ion implantation after etching the sidewall and oxide layers.
 14. The method of claim 12, further comprising performing an ion implantation prior to depositing the oxide layer.
 15. The method of claim 12, wherein re-oxidizing the polysilicon comprises performing an anneal in an inert or oxidizing ambient atmosphere.
 16. The method claim 15, wherein performing an anneal comprises performing at least one of a rapid thermal anneal, spike anneal, and ultra-high temperate anneal.
 17. The method of claim 15, wherein performing an anneal comprises performing a spike anneal at a temperature of about 900 degrees C. to about 1000 degrees C.
 18. The method of claim 15, wherein performing an anneal comprises performing a flash/laser anneal at a temperature of about 1150 degrees C. to about 1400 degrees C.
 19. The method of claim 12, wherein forming the gate comprises: depositing a gate oxide layer adjacent to the active region; depositing polysilicon layer adjacent to the gate oxide layer; and removing portions the gate oxide layer and the polysilicon layer to form the gate.
 20. The method of claim 12, wherein the oxide layer is formed to a thickness ranging from 20 Å to 70 Å.
 21. The method of claim 12, wherein the silicon oxide layer is formed to a thickness of approximately 5 Å.
 22. The method of claim 12, wherein the sidewall layer is formed of at least one material selected from the group consisting of silicon nitride (SiN), silicon carbide (SiC), silicon carbo-nitride (SiCN), silicon oxy-nitride (SiON), silicon oxy-carbide (SiOC), and silicon oxy-carbo-nitride (SiOCN). 